1. Field of the Invention
The present invention relates to an apparatus for injecting infusion fluids into a patent at a controlled infusion rate. This apparatus is referred to as a "controlled autoinfuser" A preferred embodiment of the invention comprises a computer capable of using the pressure volume relationships as defined by gas laws to generate a control signal that will control the injection of infusion fluids into a patient. In another embodiment, the present invention comprises a method of controlling the injection of infusion fluids into a patient through the use of a microprocessor controlled autoinfuser as well as a method of injecting a preselected volume of infusion fluid into a patient within a preselected infusion time without the use of a microprocessor.
2. Description of the Prior Art
Trauma is a leading cause of death in America. The optimal treatment of trauma is to stop bleeding and infuse saline solutions into the traumatized victim in order to restore blood volume, cardiac output, and pressure. Saline solutions are normally infused into peripheral vein catheters, but can also be delivered into the circulation by infusing directly into bone marrow using an intraosseous needle or intraosseous vascular access device.
Prior art infusion methods comprise the infusion of fluids to normalize cardiovascular function. One drawback of this method is that rapid increases in blood pressure can reopen clotted injuries and can increase internal bleeding and thereby actually increase mortality. As a result of this danger, some hospitals or trauma centers have policies of no prehospital resuscitation administration of fluid. This prior art method may prevent an increase in internal blood loss in many patients; however, it does not improve blood pressure and flow to those patients with cardiovascular functions below immediately life threatening critical levels.
Although it may be possible for a paramedic to monitor blood pressure or another physiological variable in order to infuse fluids as needed to reach and maintain a level of cardiovascular function necessary to sustain vital functions, such a practice requires extreme diligence on the part of the paramedic and limits or precludes the paramedic from attending to other important tasks. The present invention overcomes the weaknesses of the prior art by providing an automated means of prehospital resuscitation which does not rapidly increase blood pressure or needlessly increase internal bleeding while resuscitating the victim to a level of cardiovascular performance that maintains vital organ functions.
A variety of devices exist for infusing fluids into a body. One of such devices is a programmable infusion system, as disclosed in U.S. Pat. No. 5,078,683 to Sancoff et al. This patent discloses the use of a peristaltic pump comprising nine individual fingers which slide back and forth along a tubing segment which contains infusion fluid. Autoinfusers comprising such moving parts are complex and expensive.
Other prior art devices for the delivery of infusion fluids comprise syringe pumps. Such devices utilize a syringe wherein a piston travels through an outer cylinder containing infusion fluid in order to push the fluid Into a patient. The bottom portion of the piston comprises one or more seals to prevent infusion fluids from leaking out around the outer radial portion of the piston. Such pumps are useful for drug delivery in small volumes, but syringe size limits these pumps to volumes less than needed for resuscitation of shock. Prior art controlled infusion devices have many moving parts and require energy sources to move those parts and pump fluid.
Another limitation of current infusion pumps is that they are designed for low pressure infusion (300 mm Hg or less) needed for intravenous fluid delivery. Such pumps would be inefficient for the high pressure fluid delivery required of intraosseous fluid delivery. There is a need for a simple, less expensive controlled infusion system that can be used for intraosseous and intravenous fluid delivery in the prehospital and field environments. The size, weight, and complexity of prior art infusion devices is another drawback, particularly in field settings, as opposed to hospital settings.
Another embodiment is a method which uses the pressure volume relationship to set the initial volume, pressure and outflow resistance of a pressurized fluid container in order to deliver a total fluid volume with a predetermined flow rate or in a predetermined time interval.